IBM has taken the extraordinary step of supporting its main rival's storage products in an effort to pull back defecting customers.

Its new San Volume Controller (SVC) includes support for EMC's Symmetrix and Clariion disk arrays so all can be included in a single virtualised pool of storage. Not only does this make IBM's product more appealing to those that have shifted allegiance to EMC but should enable greater overall use of disk arrays - up to double the average of 30 percent.

The SVC is IBM's virtualisation engine inside its overall Storage Tank project.

SVC already supports Hitachi Thunder and some HP EVA arrays but, until now, not EMC arrays. It has also added support for Hitachi Lightning. The move is fulfilling a promise it made when the SVC was first announced last year. Customers can now mix and match all the main disk arrays on the market in the same SAN in the same datacentre.

The new support is the first fruits of IBM's and EMC's agreement last year to exchange storage APIs last year. EMC's PowerPath [pdf] supports EMC and IBM ESS and HDS Lightning drive arrays and hides which data is stored where from accessing servers' points of view. EMC describes it as delivering on the promise of disk virtualisation although it is not a virtualisation product.

The new SVC release will also support Windows 2003, Red Hat Enterprise Linux Advanced Server 3.0, VMware ESX 2.1 (another EMC product) and Solaris 9. Any or all of these servers together with IBM's own servers can access stored blocks on the storage arrays controlled through the SVC. It helps to prevent storage vendor lock-in.

EMC has not taken the new product with good grace however, telling the press that using IBM's SVC with its own arrays would lead to substantially degraded performance.

Unsurprisingly, IBM repudiates the suggestion. "We treat any disk as a SCSI device. Almost without exception we've improved disk throughput and performance with SVC, "Steve Cliff, sales manager for storage software in Europe, told us.

IBM's TotalStorage SAN Volume Controller v1.2 will be available from April 30th. An entry-level price with support for 2TB of storage is around £40,000.